You misunderstand my meaning. 1 single tank can disrupt or divert a portion of the backline, or if you're lucky, you can divert the entire backline. If the backline gets dived, there will be 2 common reactions, either they will scatter and flee or they will focus their attention on the person that just dived into them, in both cases, you have successfully diverted the attention of the pre-made's support group and made them that much less effective, if your team is at least aware of the fact that the 4 person pre-made is left to fend for themselves, it's very easy for them to turn it around on them, maybe take out some of their battle high.
I don't know how it is on Aether, I rarely play there, but on OCE or JP, this is a common tactic. You back off and bait the enemy team inwards, then you turn around and clean up as more of the enemy team backs away back to the objective. It just greatly weakens the power of the opposing team, which makes them easier to clean up, provided your team is of comparable skill. In the end, any skill gap is a major factor.
As for your presented problem of DRK+RPR+DRGs, Guard would not be worth it, yes, but there is another way. If you Purify the bind and Sprint away, the Hysteria from the RPR LB will likely send you out from the Sky Shatter focus point, which results in you taking much less damage. There should be time as the RPR would want to wait for the Guards to come out so they can break people out of them. On another note, another possible solution to AST stacking is to silence or stun the ASTs in the group, staggering the Macrocosmos casts, which would allow people to Recuperate in between hits and not instantly blow up.
One thing I do agree with people on DRK is that the snapshot for the pull-in on Salted Earth is very wonky since you can be pulled back in when you're already out of range before the animation even starts.
Certain people have made claims of 6+ ASTs in this very thread, you can probably find it very easily. I'm just going off what other people have said.